How to Find Gems That Depend on a Given Gem

How do I figure out which gem(s) caused a particular gem to be bundled?

Normally Gemfile.lock documents which dependencies were generated from other dependencies, it's listed in a rough tree form, but you may have to do some digging to get to the right spot.

How do I find out which gem has a specific dependency?

In the bash shell you can do:

gem dependency name_of_the_gem --reverse-dependencies

For instance:

$ gem dependency activesupport --reverse-dependencies                        
Gem activesupport-2.3.14
Used by
actionpack-2.3.14 (activesupport (= 2.3.14))
activerecord-2.3.14 (activesupport (= 2.3.14))
activeresource-2.3.14 (activesupport (= 2.3.14))

How to find out which gems depdend on gem X

gem-dependent tells you...

Ruby - How to find out all dependencies of a given Gem in a .rb file?

You can yank the code out of lib/rubygems/commands/dependency_command.rb. Here's a simple method I made.

require 'rubygems/commands/dependency_command'

def get_dependencies name, local = true
  cmd = Gem::Commands::DependencyCommand.new

  dependency = cmd.gem_dependency name, nil, nil

  specs =
  if local
    dependency.matching_specs.uniq.sort
  else
    cmd.fetch_remote_specs(dependency).uniq.sort
  end

  dependencies = []
  specs.each do |spec|
    dependencies.concat spec.dependencies.sort_by { |dep| dep.name }.map { |dep| [dep.name, dep.requirement] }
  end
  dependencies
end

puts get_dependencies('diamond_shell', false)

Command for displaying a gem's dependencies?

The following information was pulled from the rubygems command reference linked below.

http://guides.rubygems.org/command-reference/#gem-dependency

The first command you're asking for is "gem dependency". Below is the command description.

gem dependency GEMNAME [options]

Options:
-v, --version VERSION            Specify version of gem to uninstall
-r, --[no-]reverse-dependencies  Include reverse dependencies in the output
-p, --pipe                       Pipe Format (name --version ver)

Common Options:
    --source URL                 Use URL as the remote source for gems
-h, --help                       Get help on this command
    --config-file FILE           Use this config file instead of default
    --backtrace                  Show stack backtrace on errors
    --debug                      Turn on Ruby debugging

Arguments:
GEMNAME   name of gems to show

Summary:
Show the dependencies of an installed gem

Defaults:
--version '> 0' --no-reverse

The second command you'll need is "gem install". Dependencies get installed automatically. Read the quote below from the command reference for more detail.

"gem install" will install the named
gem. It will attempt a local
installation (i.e. a .gem file in the
current directory), and if that fails,
it will attempt to download and
install the most recent version of the
gem you want.

If a gem is being installed remotely,
and it depends on other gems that are
not installed, then gem will download
and install those, after you have
confirmed the operation.

Bundler: find which gem depends on this?

You could try looking inside your Gemfile.lock file.
Dependencies are nested underneath what they are required by.

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